Correlation of 1-Octen-3-one with antixenotic resistance in subterranean clover cotyledons to red-legged earth mite, Halotydeus destructor (Acarina: Penthaleidae)

Artificially damaged cotyledons of subterranean clover (Trifolium subterraneum L.) released several volatile metabolites, including 1-octen-3-one, arising from lipid peroxidation. The amount of 1-octen-3-one produced was negatively correlated with feeding damage caused by the red-legged earth mite (Halotydeus destructor) in nine out of 10 resistant and susceptible T. subterraneum varieties tested. The EC(50) of this compound in deterring mites from feeding in a membrane bioassay was 50 ppm. Cotyledon toughness was also involved in resistance. The resistant variety, S3615D, which has the lowest toughness value among the resistant varieties, produced the highest amount of 1-octen-3-one recovered from the headspace in 1 hr. Artificially damaged cotyledons of both susceptible Dalkeith and resistant DGI007, growing in shade, showed lower toughness, but had enhanced production of C-8 volatile compounds and were avoided by mites during a 3-hr feeding test. When both 1-octen-3-one content and cotyledon toughness value were taken as cofactors in resistance, the resultant multiplication value yielded a more significantly negative correlation with mite feeding damage scores within the 10 varieties than either factor alone. We conclude that 1-octen-3-one has a role in resistance of subclover cotyledon to the mite.